Food is a powerful reinforcer and the reinforcing value of food may be a determinant of food intake. There are individual differences in food reinforcement, as obese find food more reinforcing and consume more food than non-obese. The reinforcing value of food is mediated in part by the dopaminergic system, and research suggests obesity is related to the density of dopamine D2 receptors. In previous research we found smokers with high food reinforcement who had the A1 allele of the dopamine D2 receptor had increased intake of snack foods in an ad libitum eating task. This polymorphism may influence dopaminergic activity by reducing the density of dopamine D2 receptors (DRD2). We have shown a similar pattern of energy intake in pilot research with non-smokers. In addition, these pilot data have shown differences in BMI in relationship to dopamine genotypes and that obesity and dopamine genotypes interact to influence food reinforcement. This application builds upon this research to examine relationships between food reinforcement, obesity, DRD2 genotypes. Three hundred sixteen participants of mixed ethnicity and race, including an equal number of obese and non-obese males and females will be studied. Participants will be genotyped for polymorphisms of the DRD2 genotype, ad lib eating and food reinforcement measured in separate laboratory sessions, and their usual energy intake assessed by repeated 24-hour food recalls. This application provides the opportunity to determine whether 1) the A1 allele of the DRD2 genotype is associated with greater BMI and more obesity;2) food reinforcement and presence of the A1 allele of the DRD2 genotype interact to predict BMI and obesity;3) obesity is associated with increases in food reinforcement;4) obesity and the A1 allele of the DRD2 genotype interact to influence food reinforcement;and 5) ad libitum food consumption and food reinforcement in the laboratory and are related to usual energy intake. This study provides important new information on a behavioral factors that may be related to excess energy consumption, and tests how food reinforcement and the DRD2 genotype may interact in obesity. The findings are relevant to a greater understanding of behavioral and genetic factors related to obesity, as well as providing ideas that may be relevant for treatment interventions for those high in food reinforcement.